The promoting effect of sulfate ions on the nucleation of TiO2 (anatase) nanocrystals

The effect of sulfate ions on the nucleation of anatase nanocrystals during the hydrolysis of TiCl4 solution was investigated, The resulting titania powders were characterized by DSC, FT-Raman spectroscopy, X-ray diffraction and UV-Vis spectroscopy. In the presence of sulfate ions as low as one twentieth to Ti4+, the precipitate prepared at room temperature contained 17.8% anatase nanocrystalline titania. The promoting effect of sulfate ions on the nucleation of anatase at higher temperature was more significant. For example, at 343 K, anatase powder was synthesized in the presence of a small amount of sulfate ions, while mixed-phase (the fraction of rutile was 0.634) powder was prepared in the absence of sulfate ions. Small amount of sulfate ions also modified the pore size distribution effectively and stabilized anatase to convert into rutile during calcining process, and powders with narrow pore size distribution (average pore diameter 3.8 nm) and mesoporous nature were prepared in the presence of sulfate ions.